From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
To: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Jiri Olsa <jolsa@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
bpf@vger.kernel.org
Subject: [PATCH bpf v2 0/2] rethook: Reject getting a rethook if RCU is not watching
Date: Wed, 8 Jun 2022 01:10:52 +0900 [thread overview]
Message-ID: <165461825202.280167.12903689442217921817.stgit@devnote2> (raw)
Hi,
Here is the 2nd version of the patches to reject rethook if RCU is
not watching. The 1st version is here;
https://lore.kernel.org/all/165189881197.175864.14757002789194211860.stgit@devnote2/
This is actually related to the idle function tracing issue
reported by Jiri on LKML (*)
(*) https://lore.kernel.org/bpf/20220515203653.4039075-1-jolsa@kernel.org/
Jiri reported that fprobe (and rethook) based kprobe-multi bpf
trace kicks "suspicious RCU usage" warning. This is because the
RCU operation is used in the kprobe-multi handler. However, I
also found that the similar issue exists in the rethook because
the rethook uses RCU operation.
I added a new patch [1/2] to test this issue by fprobe_example.ko.
(with this patch, it can avoid using printk() which also involves
the RCU operation.)
------
# insmod fprobe_example.ko symbol=arch_cpu_idle use_trace=1 stackdump=0
fprobe_init: Planted fprobe at arch_cpu_idle
# rmmod fprobe_example.ko
=============================
WARNING: suspicious RCU usage
5.18.0-rc5-00019-gcae4ec21e87a-dirty #30 Not tainted
-----------------------------
include/trace/events/lock.h:37 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
RCU used illegally from extended quiescent state!
no locks held by swapper/0/0.
stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.18.0-rc5-00019-gcae4ec21e87a-dirty #30
------
After applying [2/2] fix (which avoid initializing rethook on
function entry if !rcu_watching()), this warning was gone.
------
# insmod fprobe_example.ko symbol=arch_cpu_idle use_trace=1 stackdump=0
fprobe_init: Planted fprobe at arch_cpu_idle
# rmmod fprobe_example.ko
fprobe_exit: fprobe at arch_cpu_idle unregistered. 225 times hit, 230 times missed
------
Note that you can test this program until the arch_cpu_idle()
is marked as noinstr. After that, the function can not be
traced.
Thank you,
---
Masami Hiramatsu (Google) (2):
fprobe: samples: Add use_trace option and show hit/missed counter
rethook: Reject getting a rethook if RCU is not watching
kernel/trace/rethook.c | 9 +++++++++
samples/fprobe/fprobe_example.c | 21 +++++++++++++++++----
2 files changed, 26 insertions(+), 4 deletions(-)
--
Signature
next reply other threads:[~2022-06-07 16:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-07 16:10 Masami Hiramatsu (Google) [this message]
2022-06-07 16:11 ` [PATCH bpf v2 1/2] fprobe: samples: Add use_trace option and show hit/missed counter Masami Hiramatsu (Google)
2022-06-17 16:06 ` Steven Rostedt
2022-06-22 1:41 ` Masami Hiramatsu
2022-06-07 16:11 ` [PATCH bpf v2 2/2] rethook: Reject getting a rethook if RCU is not watching Masami Hiramatsu (Google)
2022-06-17 16:19 ` Steven Rostedt
2022-06-17 11:27 ` [PATCH bpf v2 0/2] " Jiri Olsa
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